Data Signals; Strobe Signals; Href Generation/Distribution - Intel 815EG Design Manual

Chipset platform for use with universal socket 370

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Hub Interface

9.1.1

Data Signals

Hub interface data signals should be routed with a trace width of 5 mils and a trace spacing of

20 mils. These signals can be routed with a trace width of 5 mils and a trace spacing of 15 mils for

navigation around components or mounting holes. To break out of the GMCH and the ICH2, the

hub interface data signals can be routed with a trace width of 5 mils and a trace spacing of 5 mils.

The signals should be separated to a trace width of 5 mils and a trace spacing of 20 mils, within

0.3 inch of the GMCH/ICH2 components.

The maximum trace length for the hub interface data signals is 8 inches. These signals should each

be matched within ±0.1 inch of the HL_STB and HL_STB# signals.

9.1.2

Due to their differential nature, the hub interface strobe signals should be 5 mils wide and routed

20 mils apart. This strobe pair should be a minimum of 20 mils from any adjacent signals. The

maximum length for the strobe signals is 8 inches, and the two strobes should be the same length.

Additionally, the trace length for each data signal should be matched to the trace length of the

strobes, within ± 0.1 inch.

9.1.3

HREF, the hub interface reference voltage, is 0.5 * 1.85 V = 0.92 V ± 2%. It can be generated

using a single HREF divider or locally generated dividers (as shown Figure 55 and Figure 56). The

resistors should be equal in value and rated at 1% tolerance, to maintain 2% tolerance on 0.92 V.

The values of these resistors must be chosen to ensure that the reference voltage tolerance is

maintained over the entire input leakage specification. The recommended range for the resistor

value is from a minimum of 100 Ω to a maximum of 1 kΩ (300 Ω shown in example).

The single HREF divider should not be located more than 4 inches away from either GMCH or

ICH2. If the single HREF divider is located more than 4 inches away, then the locally generated

hub interface reference dividers should be used instead.

The reference voltage generated by a single HREF divider should be bypassed to ground at each

component with a 0.01 µF capacitor located close to the component HREF pin. If the reference

voltage is generated locally, the bypass capacitor must be close to the component HREF pin.

Intel

815EG Chipset Platform Design Guide

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